Navy Yard Shooting Update: 12 people confirmed dead after Washington Navy Yard rampage

Updated 3:05 p.m. (CBS/AP) WASHINGTON D.C. - Twelve people are confirmed dead after a shooting at the Washington Navy Yard Monday morning, Metropolitan Police Chief Cathy Lanier said at a press conference Monday afternoon.

PICTURES: Washington Navy Yard shooting

A gunman was confirmed dead, and Lanier said two other possible suspects who could be involved in the shooting are still at large, men she said were seen with weapons wearing military-style uniforms.

Following the press conference, however, the Metropolitan Police Department tweeted that one of the men had been located and cleared as a suspect or person of interest. He had initially been described by Lanier as a white man in a tan military-style outfit, apparently carrying a handgun.

Police are still searching for a second possible suspect, whom Lanier as a black male, between 40 and 50 years old in an olive military-style uniform, about five feet, ten inches tall and 180 pounds. The man had gray sideburns, Lanier said.

An active search is continuing and could span several hours, Lanier said. She urged residents around the Navy Yard to stay clear of the scene.

Police are asking anyone with information on these two people to call 202-727-9099.

Lanier couldn't provide more information about the identity of the gunman who was killed.

The shooting was reported around 8:20 a.m. Monday morning at the Naval Sea Systems Command Headquarters building. Multiple local, state and federal agencies responded, and Lanier described their actions as "nothing short of heroic."

Earlier, she said he may have been armed with a long gun.

Police haven't reported a motive.

Several others were reported wounded. Speaking to reporters, Dr. Janis Orlowski, the chief medical officer at MedStar Washington Hospital Center, said that three victims had been transported to her hospital, and all were alert and expected to survive.

One of the victims was a male Metropolitan police officer who suffered multiple gunshot wounds to his legs, Orlowski said.

Another victim, a woman, suffered gunshot wounds to her head and hands, and a third victim, also a woman, suffered a gunshot wound to her shoulder.

Orlowski said the hospital was told to expect more victims but it wasn't clear whether more would be transported.

Police and emergency crews gathered Monday morning outside the heavily-guarded Naval Sea Systems Command Headquarters building, where the shooting was reported.

Witnesses described a gunman opening fire from the fourth floor, aiming down on people in the first-floor cafeteria. Others said a gunman fired at them in a third-floor hallway.

Patricia Ward, who works at the Navy Yard, told reporters that she was in the cafeteria when she head three shots in quick succession and then four more shots.

"A lot of people were just panicking," Ward said. "No screams or anything, because we was just in shock."

The Navy says about 3,000 people work in the building. People inside the building have been directed to stay in place.

In a press release, the Navy said the shooting happened at approximately 8:30 a.m. ET.

United States Capitol Police said they are "providing mutual support & assistance to the Metropolitan Police Department" in a press release. They say the active shooter incident is "contained to the Navy Yard."

According to USCP, "Additionally, people may notice enhanced security operations being conducted by the USCP on the Capitol Grounds as a proactive, precautionary measure related to the active shooter incident at the Navy Yard."

Naval Sea Systems Command is the largest of the Navy's five system commands and accounts for a quarter of the Navy's entire budget.

It builds, buys and maintains the Navy's ships and submarines and their combat systems.